Sterile optical sensor system having an adjustment mechanism

ABSTRACT

Systems, methods and a sensor alignment mechanism are disclosed for medical navigational guidance systems. In one example, a system to make sterile a non-sterile optical sensor for use in navigational guidance during surgery includes a sterile drape having an optically transparent window to drape the optical sensor in a sterile barrier and a sensor alignment mechanism. The alignment mechanism secures the sensor through the drape in alignment with the window without breaching the sterile barrier and facilitates adjustment of the orientation of the optical sensor. The optical sensor may be aligned to view a surgical site when the alignment mechanism, assembled with the sterile drape and optical sensor, is attached to a bone. The alignment mechanism may be a lockable ball joint and facilitate orientation of the sensor in at least two degrees of freedom. A quick connect mechanism may couple the alignment mechanism to the bone.

CROSS REFERENCE

The present application is a continuation of U.S. Ser. No. 13/833,181filed Mar. 15, 2013 and entitled “System and Method for Intra-OperativeLeg Measurement”, the contents of which are herein incorporated byreference.

TECHNICAL FIELD

The present disclosure relates generally to sterile surgical equipment.In particular the present disclosure relates to sterile optical sensorsystem having an adjustment mechanism to permit orientation of thesensor to view a surgical site.

BACKGROUND

In many surgical procedures, including joint replacement such as TotalHip Arthroplasty (THA), achieving precise positioning of tools andimplants with respect to a patient's anatomy is critical for successfuloutcomes. FIG. 1 illustrates a pre-operative 100 and post operative 102hip joint, along with a coordinate frame defining various directions104. The post-operative hip joint is composed of a femoral component 106and an acetabular component 108. In one THA technique, the hip joint isexposed and dislocated. The acetabulum and the femur are prepared forreceiving implants. Typically, a cup prosthesis is to be implanted inacetabulum requiring alignment of the cup with respect to the patient'sanatomy. Trial femoral prosthetics—available in various sizes tofacilitate intra-operative adjustment—may be implanted to assess thecorrect final femoral implant size. The fit and sizing of the joint maybe iteratively assessed and a final prosthetic hip joint (106 and 108)implanted.

Positioning prosthetic implants relative to the patient's anatomy mayinvolve numerous challenges such as, selecting the correct implantgeometry and altering the patient's bony anatomy (e.g. reaming,osteotomy, etc.), among others. Some important goals for a successfulTHA include: proper alignment of the acetabular cup; restoration orcorrection of leg length and offset; restoration of hipcenter-of-rotation (COR); and stability of new hip joint. The concept ofleg length and offset change seems simple at first; however, it is acomplex clinical and geometrical problem. The surgeon is often requiredto make various accurate assessments of leg length and offsetintra-operatively.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of embodiments of the systems, methods anddevices described herein, and to show more clearly how they may becarried into effect, reference will be made, by way of example, to theaccompanying drawings in which:

FIG. 1 is an illustration of a hip before and after THA includinganatomical references frames in accordance with the prior art;

FIG. 2 is an example of a system for determining and presenting leglength and offset measurements intra-operatively;

FIG. 3 is a process chart showing operations for use of leg length andoffset measurement in accordance with an example;

FIGS. 4 and 5 are screen shots of a representative graphical userinterface showing leg length and offset registration and measurements inaccordance with an example;

FIG. 6 is a flow chart of operations of a workstation or otherprocessing unit to provide leg length and offset measurement inaccordance with an example;

FIG. 7 is a screen shot of a representative graphical user interfaceshowing sensor and target alignment in accordance with an example;

FIG. 8A is an exploded view of a pelvic clamp assembly in accordancewith and example with a sterile drape with integrated optical window;

FIG. 8B is an end view of the pelvic clamp of FIG. 8A shown assembledwith the sterile drape and a sensor;

FIG. 9 shows components of a pelvic platform in accordance with anexample;

FIG. 10 shows a femur platform with femur screw in accordance with anexample;

FIGS. 11A and 11B show an example quick connection mechanism;

FIG. 12 shows a beacon component in accordance with an example;

FIGS. 13A and 13B show respective front and back sides of a planartarget, in accordance with an example, such as for mounting on beaconcomponent of FIG. 12; and

FIG. 14 shows a sensor in accordance with an example.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity.

DETAILED DESCRIPTION

Pertaining to leg length and offset, with reference to FIG. 1, leglength change is defined as the change in femur position in thesuperior-inferior direction (i.e., if the femur translates in theinferior direction as a result of surgery, a positive leg length changehas occurred). A leg length change may occur due to acetabular componentplacement, femoral component placement or sizing, or a combination ofboth. Note that in this figure, the femur and pelvis are aligned suchthat they have zero relative flexion, rotation and abduction. Thisrelationship is said to be “neutral”. If the femur was not neutral withrespect to the pelvis, then the coordinate frame of the femur would notalign with the pelvis, but rather be rotated by the same amount as thefemur; for example, if the femur were abducted by 90 degrees, then thefemur's inferior direction would be the pelvis' lateral direction. Inthis case, it is clear that the total leg length change is the leglength change due to the acetabular component position (in the pelviscoordinate frame) summed with the leg length change due to the femoralcomponent position (in the femur coordinate frame). It is also clearthat, when neutral, both frames align, simplifying the problem.

Offset change is analogous to leg length change; however, it is in thelateral-medial direction (i.e. if the femur translates laterally as aresult of the surgery, then a positive offset change has occurred).Occasionally in the art of hip arthroplasty, offset is not definedpurely in the medial-lateral direction (in the patient's coronal plane),but rather in a plane rotated about the patient's mid-line by the amountof femoral version (typically 10-15 degrees). The femoral prostheticdoes not sit purely in the medial-lateral plane; it is rotated (withreference to FIG. 1) slightly forward, such that the ball sits moreanteriorly than the stem. This alternative definition of offset would beas if the femur were internally rotated (by approximately 10-15 degrees)such that the femoral prosthetic was purely in the coronal plane.

Some technical terms and definitions will be useful throughout thisdocument. The art of tracking is chiefly concerned with positions andorientations. The terms “coordinate system”, “coordinate frame”,“reference frame”, etc, refer to a standard basis in which positions andorientation may be described. The terms “pose” (position and orientationstate estimate), position, relative position, spatial positioning, etc,all refer to describing the position and/or orientation of a rigid bodywith respect to some coordinate frame.

There are provided systems, methods and computer program products fornavigational guidance systems. In one example, intra-operative legposition measurements are provided during hip arthroplasty. Provided isan optical sensor for coupling to a pelvis and a target for coupling toa femur in alignment with the sensor. The sensor provides positionalsignals to a processing unit for determining a relative position of thesensor and target. The processing unit is configured to use a baselinemeasurement of leg position and a map to calculate and display legposition measurements in real time. The map is defined through aregistration range-of-motion (RROM) procedure where instructions arepresented for moving the femur in at least two planes to generatesignals to calculate the map. Leg position may be leg length and/oroffset and/or anterior-posterior position of the leg. The map is used topresent the leg position measurements in an anatomical, rather than asensor, coordinate frame.

There is disclosed a system for providing intra-operative leg positionmeasurements during hip arthroplasty of a pelvis and a femur at asurgical site. The system comprises: an optical sensor for coupling tothe pelvis and for alignment with the surgical site: a target forcoupling to the femur in alignment with the sensor, the sensor providingsignals in response to the target for determining relative positions ofthe sensor and target; and a processing unit for communicating with thesensor, the processing unit configured to use a baseline measurement ofleg position and a map to calculate and display leg positionmeasurements in real time, where the map is defined through aregistration range-of-motion (RROM) procedure. The processing unit mayreceive first signals from the sensor and determines the relativeposition of the sensor and target to determine the baseline measurement,a plurality of second signals generated through the RROM to define themap and a plurality of third signals to display leg positionmeasurements in real time using the baseline measurements and the map.The processing unit may present instructions, via a graphical userinterface, for moving the femur in at least two planes to generate theplurality of second signals during the RROM procedure. In one example,the leg position is leg length and offset. The processing unit may usethe map to present the leg position measurements in an anatomicalcoordinate frame. The leg position measurements can be displayedindependently of an orientation of the femur. In one example, theprocessing unit is further configured to detect hip joint subluxation inreal time and alert in accordance with the detection.

There is disclosed a method for performing a hip arthroplasty withintra-operative digital leg position guidance comprising: determiningand storing a pre-dislocation baseline femur position by a processingunit using a sensor and a target providing signals for determining arelative position; performing a registration range of motion (RROM)procedure, after a prosthetic joint reduction, by the processing unit todefine a RROM map to an anatomical coordinate frame for leg positionmeasurements generated using the signals; and displaying leg positionmeasurements in real-time on a display using the baseline femur positionand RROM map. The method may comprise receiving the signals by theprocessing unit in response to an intra-operative movement of the femurand calculating the leg position measurements for intra-operativedisplay. In one example, the method may comprising detecting andalerting of hip joint subluxation by the processing unit in response tothe leg position measurements. A computer program product aspect is alsodisclosed in which there is a computer program product for performing ahip arthroplasty with intra-operative digital leg position guidancecomprising non-transitory medium storing instructions and data forconfiguring the execution of a processing unit to perform such as inaccordance with the method.

There is disclosed a system to provide intra-operative guidance during amedical procedure comprising: a single sensor, for coupling to a boneand orienting toward a site for the medical procedure; a single target,coupled to an object, for tracking by the sensor; and, a processing unitfor communicating with the sensor, the processing unit displaying arelative position of the object and the bone, in accordance with arelative position of the target and the sensor calculated using thepositional signals from the sensor. The bone may be a pelvis. The objectmay be a femur. The processing unit can calculate a registration byprompting movement of the object while collecting pose data. The medicalprocedure may be a surgical procedure, for example, a hip arthroplastyprocedure. In one example, the bone is a pelvis and the object is afemur and the processing unit calculates a leg length and offset changemeasurement intra-operatively.

There is disclosed a method to provide intra-operative guidance during amedical procedure comprising: receiving at a processing unit a pluralityof positional signals from a single sensor coupled to a bone andoriented toward a site for the medical procedure, the positional signalsgenerated for a single target, coupled to an object, for tracking by thesensor; calculating by the processing unit a relative position of theobject and the bone in accordance with the positional signals; andintra-operatively displaying the relative position on a display. Thebone may be a pelvis. The object may be a femur. The method may includecalculating, by the processing unit, a registration by promptingmovement of the object while collecting pose data. The medical proceduremay be a surgical procedure, for example, a hip arthroplasty procedure.In one example, the bone is a pelvis and the object is a femur and themethod further comprises calculating, by the processing unit, a leglength and offset change measurement intra-operatively.

There is disclosed a computer program product comprising anon-transitory medium storing instructions and data for configuring theexecution of a processing unit to receive a plurality of positionalsignals from a single sensor coupled to a bone and oriented toward asite for the medical procedure, the positional signals generated for asingle target, coupled to an object, for tracking by the sensor;calculate a relative position of the object and the bone in accordancewith the positional signals; and intra-operatively display the relativeposition on a display.

There is disclosed a medical navigational guidance system comprising: asensor for coupling to a bone and orienting toward a site for a medicalprocedure; a target, coupled to an object, for tracking by the sensor;and, a processing unit in communication with the sensor, the processingunit configured to guide alignment of the sensor with the target, theprocessing unit using positional signals from the sensor to calculateand display, using a user interface, directional instructions to moveinto alignment the sensor and target. The system may comprise analignment mechanism facilitating two degrees of freedom orientationadjustment of the sensor with respect to the bone. The alignmentmechanism may be a locking mechanism to releasably fix the orientationof the sensor. The alignment mechanism is a lockable ball joint. Thetarget may be used to define the location of the site. The processingunit may represent the pivoting orientation of the sensor as a crosshairon a display screen and the location of the surgical site as a bull'seye target. The system may comprise a releasable coupling for couplingthe sensor to the bone.

There is disclosed a method of performing a medical procedure undernavigational guidance comprising guiding, using a processing unit and adisplay, the alignment of a sensor configured to track a target at asite for the procedure, the processing unit receiving positional signalsfrom the sensor and calculating and displaying, using a user interface,directional instructions to move into alignment the sensor and target.The sensor may be coupled to a bone and is capable of pivotingorientation in at least two degrees of freedom not including pivotingabout an optical axis of the sensor. The pivoting orientation islockable to maintain alignment. The processing unit signals to lock thepivoting orientation in response to the alignment. The target may beused to define the site. The method may comprising displaying thepivoting orientation of the sensor in 2 degrees of freedom. The userinterface may indicates the location of the surgical site in 2 degreesof freedom. In one example, the user interface represents pivotingorientation of the sensor as a crosshair on the display screen, and thelocation of the surgical site as a bull's eye target. The bone may be apelvis. The target may be placed on a femur.

There is disclosed a computer program product comprising anon-transitory medium storing instructions and data for configuring theexecution of a processing unit to perform guiding, using a display, thealignment of a sensor configured to track a target at a site for amedical procedure, the processing unit receiving positional signals fromthe sensor and calculating and displaying directional instructions tomove into alignment the sensor and target.

There is disclosed a system for making sterile a non-sterile sensor foruse in navigational guidance during surgery. The system comprises: asterile drape having an optically transparent window for draping thesensor in a sterile barrier; a shroud, which when engaged with a drapedoptical sensor, secures the sensor through the drape in alignment withthe window without breaching the sterile barrier; and a clamp, which, inits closed and position, is configured to rigidly hold the assembledshroud, drape and sensor, while preserving the optical sensor alignmentin the window. The shroud and the clamp may have respective matingsurfaces which, when the sensor is in the shroud and the clamp is in apartially closed position, enable relative movement of the shroud andclamp to adjust the orientation of the sensor. The respective matingsurfaces may define portions of respective spheres. The clamp isconfigured for coupling to a bone, for example, using a releasable quickconnect mechanism. A method aspect therefor is also disclosed.

A method and system for surgical tracking has been presented inApplicant's U.S. patent application Ser. No. 13/328,997 filed Dec. 16,2011 and entitled “Method And System For Aligning A Prosthesis DuringSurgery”, which application published as Publication No. 2012/0157887dated Jun. 21, 2012, the content of which is incorporated herein in itsentirety. This method and apparatus obviates the requirement for astationary, fixed baseline stereo camera located outside the surgicalfield; instead, an optical sensor combined with a target are fixeddirectly to the patient's anatomy and surgical instruments within thesurgical field. This architecture is well-suited to measure relativepose, since the sensor is directly coupled to one of the objects beingtracked. It is also well-suited toward surgical applications, whichtypically have a relatively small surgical working volume. This methodand apparatus for positional tracking can be applied to various surgical(and in particular, orthopaedic) procedures. In particular, it may beused during THA to provide intra-operative guidance to the surgeon forleg length and offset.

With reference to FIG. 2 herein, one example system in which a sensor isdirectly coupled to one of the objects being tracked is a system 200,which provides intra-operative leg length and offset change measurements(e.g. determining relative positions, monitoring changes and presentingmeasurements) to a surgeon. In this system 200, a goal is to measure leglength and offset (from references on the pelvis and femur) inreal-time. There is a sensor 202 coupled to the patient's pelvis 204 viaa pelvic clamp 206 and a pelvic platform 208. The pelvic platformprovides a mechanically rigid connection to the pelvis, for example,using bone pins or screws. The pelvic clamp has three functionalcharacteristics: to attach the sensor to the pelvic platform; to providea means to aim the sensor towards the surgical site (when attached topelvic platform); and, to provide a repeatable quick-connection pointbetween the pelvic platform and the pelvic clamp/sensor assembly (suchthat the surgeon may remove this assembly when not in use, or as a firstpoint of failure in case of an unintended mechanical blow).

Again, in reference to FIG. 2, there is a target 210 coupled to thefemur 212 via a beacon 214 and a femur platform 216. The femur platformprovides a mechanically rigid connection to the femur, for example,using bone pins or screws. The beacon has two functionalcharacteristics: to attach the target to the femur platform, and toprovide a repeatable quick connection point between the femur platformand the beacon/target assembly (such that the surgeon may remove thisassembly when not in use, or as a first point of failure in case of anunintended mechanical blow).

There is symmetry in this system's architecture on the pelvic andfemoral sides. The following system components are analogous, in thesense that they fundamentally serve similar functions: pelvic and femurplatforms are used for rigid connections to bone; pelvic clamp andbeacon are used to interface to their respective platforms, provide aquick connection, and attach to the sensor/target; the sensor and targetare the tracking system components, which are simultaneously used tomeasure their relative pose. Having such symmetry and structure in thisdevice is advantageous. It simplifies mechanical design, manufacture andtolerance analysis (e.g. the same quick-connection mechanism may be usedon both pelvic and femoral sides). It also provides modularity andflexibility (e.g. a different beacon design can be implemented withoutchanging the femur platform or target designs), which is highlyimportant when considering additional surgical applications (forexample, knee arthroplasty).

Within the operation of the tracking system 200, the sensor 202 sensesthe target 210, and provides an output to a workstation 218 or otherprocessing unit (e.g. by any means of communication, for example, USB)for processing by a processor or processors (not shown) such as may beconfigured by a computer program or programs 220 (e.g. one or moreapplications, operating systems, etc. or other software, instructionsand/or data) stored to a computer medium (not shown), such as anon-transitory medium, for execution by the processor or processors inorder to determine the pose between the target 210 and the sensor 202(and hence, the pelvis and the femur). It will be appreciated that thedescription of the workstation is simplified. In another exampleembodiment, the methods are implemented primarily in hardware using, forexample, hardware components such as application specific integratedcircuits (ASICs). Implementation of the hardware state machine so as toperform the functions and methods described herein will be apparent topersons skilled in the relevant art(s). In yet another embodiment, themethods are implemented using a combination of both hardware andsoftware.

In particular, the sensor 202 is optical, and the sensor output signalsrepresent a 2-dimensional image. The target is visible to the opticalsensor, and has an identifiable pattern. By processing the image outputof the sensor, and with a priori knowledge of the target's patterngeometry, the workstation 218 is able to calculate relative pose. Inaddition to calculating relative pose, the workstation 218 may displayinformation to a surgeon via a Graphical User Interface (GUI) inreal-time such as presenting information via a display 222.Representative screen shots in accordance with an example are describedherein below. This information may be displayed in any coordinate frame;however, it is preferable to display pose information to a surgeon in ananatomical coordinate frame. The software workflow preferably cooperateswith the surgical workflow, and may: prompt the surgeon to performcertain actions, collect certain data, verify integrity of data, detecterrors, display data at clinically appropriate times, log data, etc.

In the present example, the positional navigation system relies on onesensor and one target only, in order to provide intra-operative leglength/offset measurements. This is a reduction in complexity relativeto existing computer navigation systems, which have fundamentalrequirements to: process multiple images (stereo camera) and trackmultiple objects simultaneously (pelvis, femur, stylus/otherinstruments).

FIG. 3 is a process chart that describes a method of using system 200 inorder to intra-operatively measure and display changes in leg length andoffset to a surgeon during THA. During “Set-up” 302, the system isprepared for use. This step 302 may occur while the surgical personnelare performing their standard surgical preparation, immediately prior tothe operation. In step 302, the workstation 218 is set-up in anappropriate location and powered on. The sensor 202 is connected. Sincethis is a surgical device, the components of the system which are usedwithin the sterile field are provided sterile (whether terminallysterile, protected with a sterile drape, or re-processed within thehospital). Also, in step 302, the beacon 214 and target 210 areassembled. At the conclusion of this step, the system 200 is ready foruse.

The objective of the next step 304, called “Baseline”, is to determineand store a pre-operative leg length and offset reference. This step 304occurs preferably immediately prior to the dislocation of the native hipjoint, after the hip is surgically exposed. The femur platform 216 andpelvic platform 208 are mounted to their respective bones, in order toprovide rigid structures for the sensor 202 and target 210 of the system200. The beacon 214 (coupled with the target 210) is preferably mountedonto the femur platform 216. The sensor 202 is then placed within thepelvic clamp 206. Initially, the sensor 202 may have its orientationwithin the pelvic clamp 206 adjusted. In order to align the sensor 202with the surgical site, the software 220 (via a graphical user interfaceon display 222) may guide the surgeon to align the orientation of thesensor 202 based on the pose of the target 210 (mounted on the femur,which represents the position of the surgical site). Upon suitablealignment, the surgeon may lock the pelvic clamp 206 and sensor 202 inplace, such that the orientation is no longer adjustable. At this time,the system 200 is prepared to determine and store a pre-operative leglength and offset reference.

The desired pre-operative leg length and offset reference is used as abasis to compute change in leg length and offset. This referencemeasurement is a pose, and may be triggered by the surgeon (e.g. bypressing a button located on the sensor 202). Note that the referencemeasurement (pose) is not expressed in anatomical coordinates (since noregistration procedure has occurred yet), but rather in the sensor 202coordinate frame. This reference baseline pose is stored by the software220 for later use. The system 200 measures changes in leg length andoffset; it is up to the surgeon and their pre-operative planning todetermine their desired values of leg length and offset change(typically done by analyzing left and right hips using pre-opradiographs). Note that during baseline measurement, it may be necessaryfor the femur to be substantially “neutral” with respect to the pelvis;this means that the femur coordinate frame is aligned with the pelviccoordinate frame, or in clinical terms, that the femur has zero flexion,zero adduction and zero rotation (it is possible to alleviate thisrequirement where a femur registration is explicitly performed, and whenthe pre and post operative COR are known).

After a baseline measurement of leg length and offset is recorded, thesurgeon may proceed with the hip arthroplasty. The beacon 214 (withtarget 210) and pelvic clamp 206 (with sensor 202) may be removed usingtheir respective quick connections, so as not to clutter the surgicalsite (leaving the low-profile pelvic platform 208 and femur platform 216in place).

Typically, surgeons perform a first trial reduction using a finalacetabular shell with trial components (e.g. liner, broach neck, head).It is at this time when the function of the prosthetic hip joint isassessed, including assessing the resulting change in leg length andoffset. Normally surgeons unequipped with computer navigation assess thechange in leg length and offset using ad hoc techniques.

In order for the system 200 to provide meaningful real-time measurementsof leg length and offset to the surgeon, a registration must occur.Registration refers to a process in which the map between the trackingsystem's coordinate frame (i.e. the sensor 202) and the patient'sanatomical coordinate frame is determined. It is known to performregistration when using known fixed stereo camera-based positionalnavigation systems. Such registration is normally accomplished with atracked “probe” or “stylus”, which contacts anatomical landmarks, andreconstructs the patient's anatomical coordinate frame in this manner.The systems (e.g. 200) and methods described herein can accommodate“probe” or “stylus” based registration; however, operation without useof a probe or stylus may be preferred.

In reference to step 306 (“Registration”) a registration procedureinvolving moving the femur in pre-defined and known motions (with thesensor 202 and target 210 attached in their respective anatomicallocations) is used to map the patient's anatomy. This procedure will bereferred to as the Registration Range-of-Motion (RROM). The RROMprocedure may be advantageous for the following reasons:

-   -   it obviates the need for an additional system component for        registration (e.g. tracked stylus);    -   the surgeon typically performs a clinical range-of-motion test        contemporaneously (i.e. this method of registration matches the        existing surgical workflow);    -   the pre-defined motions are well-known in clinical terminology        and practice;    -   the RROM data is also used to calculate the hip COR (no        additional data necessary)

In particular, the RROM procedure may prompt the surgeon to move thefemur in flexion/extension, internal/external rotation, and/orabduction/adduction, while the sensor 202 (coupled to the pelvis), inconjunction with the software 220, tracks the pose of the target 210(coupled to the femur). For example, the GUI on display 222 may promptthe surgeon to move the femur in the flexion-extension direction; sincethis motion lies in a plane, the pose tracking data may be furtherprocessed by the software 220 in order to determine the equation of theplane in the sensor's 202 coordinate frame. In order to determine thepatient's principal anatomical reference frame (and hence, resolvemeasurements into leg length and offset coordinates), it is preferred tocollect tracking system pose data of at least two planes (since anorthogonal reference frame can be determined from two planes). Anexample of the workstation 218 (e.g. software) prompting the surgeonduring the RROM procedure is found in the GUI of FIG. 4. Here, thesurgeon is prompted to move the leg in pre-defined motions, as shown inthe instructional graphic 402 (note that the instructional graphic doesnot necessarily show the patient's anatomy, but rather a genericrepresentation of a pelvis and a femur and portions of system 200 thatis intended to be instructional). The motions are described in clinicalterms 404. During the execution of the motions, the workstation 218accumulates pose data until a sufficient amount is collected, asindicated by the progress bars 406. The amount of pose data is deemedsufficient when there is a high confidence that the pose data associatedwith each motion will yield an accurate anatomical feature (i.e. plane);for example, in order to mitigate random noise and outliers, a minimumnumber of pose data points, including a minimum variance in pose, may berequired.

In further reference to the GUI of FIG. 4, a navigation panel 408 isshown, which is intended to provide a surgeon with an indication oftheir current step in the process. Also, further instructionalindicators 410 are shown. The indicators 410 correspond to user inputs(for example, buttons on sensor 202) which the surgeon interacts with,and the labels provide instruction on the action resulting from eachuser input. For example, in this case, one user input might cause thesystem 200 to go back to the previous step (as indicated in thenavigation panel 408), whereas another user input might trigger anaction in accordance with the current step in the process (e.g. triggerthe collection of RROM pose data). The navigation panel 408 andinstructional indicator 410 may persist throughout the various stagesand GUI's of the software 220.

The RROM procedure 306 occurs after the trial reduction, meaning thatthe acetabular cup or shell has already been implanted. Not only is thisadvantageous since it matches the existing surgical workflow, but theprosthetic joint will facilitate a smooth motion, whereas a native hipjoint might not (e.g., due to flexion contractures, bony impingement,arthritic deformities, etc).

At the conclusion of the RROM procedure, the software has calculated amap from the patient's coordinate frame to the sensor 202, as well asthe position of the hip COR (with respect to the sensor 202). Bothpieces of information are useful for the “Real-time Guidance” step 308.In this step, real-time measurements of leg length and offset areprovided to the surgeon via the GUI on the display 222. For example,FIG. 5 shows a graphical user interface including a display of leglength and offset change 502 (updating in real-time), as well assnapshots of leg length and offset changes 504, which may be captured atthe surgeon's discretion (for example, to aid in keeping track ofnumbers amongst several joint reductions), for example, by pressing the“record” button on the sensor 202. The surgeon may use the real-time leglength and offset information to select trial and final implant sizes tomeet their desired pre-operatively planned leg length and offsetchanges. Note that the transition from the GUI of FIG. 4 to the GUI ofFIG. 5 may be configured to occur automatically, at the conclusion ofthe Registration step 306.

During the “Real-time Guidance” step 308, measurements of leg length andoffset change are not influenced by the femur's orientation. This issignificant, because other existing products are very sensitive toreturning the femur to the original baseline orientation in order tomaintain accuracy. In this system and method, the RROM calculates thepatient's anatomical coordinate frame and hip COR, which facilitates a“virtual” realignment of the femur, however it is oriented, with thebaseline measurement orientation. In simple terms, this system andmethod automatically compares “apples to apples” when calculating leglength and offset change.

In the “Clean up” step 310, the device is removed from the patient,single-use components are discarded, other components are powered down,cleaned, stowed, etc. This step occurs after the surgeon is satisfiedwith the leg length and offset change effected, and/or after the finalprosthetic hip joint has been implanted.

FIG. 6 is a flow chart of operations of workstation 218 to provide leglength and offset measurement in accordance with an example. Thesoftware, which is a part of system 200, executes on the workstation andprovides functions and work flow that cooperate with the clinicalworkflow, as outlined in FIG. 3. In step 602, the software isinitialized and made ready for use. For example, the surgeon or anotheruser may select an operative hip (right or left), as well as ensure thatthe sensor 200 is plugged in and operational. The surgeon may thenadvance the software.

After the initial incision and installation of the femur platform 216,beacon 214, target 210, pelvic platform 208 and pelvic clamp 206, thesensor 202 may be aligned and secured. In step 604, the software 220guides the surgeon in aligning (and securing) the sensor 202 such thatit is aimed at the surgical site. This may be accomplished via a GUI, asshown in FIG. 7. This GUI uses a “bull's eye” graphic 702 and real-timealignment indicator 704, shown as crosshairs, such that the surgeon isprompted to hit the “bull's eye” 702 with the crosshairs 704, byadjusting the angle of sensor 202, as indicated by the instructionalgraphic 706. The angle of the sensor 202 is preferably adjustable in atleast two rotational degrees of freedom which facilitate its alignmenttoward the surgical site (i.e. rotating the sensor 202 about its opticalaxis will not help; the other two rotational degrees of freedom arerequired to align the sensor 202 with the surgical site). The basis foralignment may be the pose of the target 210, coupled to the patient'sfemur, as shown in the instructional graphic 706. The target 210 may beused in other ways to serve as a basis for alignment (e.g. manuallyholding the target 210 in the center of the surgical volume). Once thesensor 202 is appropriately aligned with the surgical site, based on thepose of the target 210, the surgeon preserves this alignment bymechanically locking the sensor in place.

Once the sensor 202 is aligned (and the surgeon has advanced thesoftware), and prior to hip dislocation, a baseline pose measurement istaken, as indicated in step 606. During the baseline measurement, thefemur is held in a neutral position with respect to the pelvis. Thebaseline pose is stored in the memory of the workstation 218, forexample, for accessing later in the procedure. At this point, thesurgeon may advance the software and remove the sensor 202 (along withpelvic clamp 206, as well as target 210 (with beacon 214) and proceedwith the surgery until they are ready to assess intra-operative leglength and offset, at which point the sensor 202 (along with pelvicclamp 206), as well as target 210 (with beacon 214) are replaced on thepatient. In one example, the pelvic clamp 206 may be attached to arepeatable mechanical connection on the pelvic platform 208 and thebeacon may be attached to a repeatable mechanical connection on thefemur platform 216. At this time, as indicated in step 608, the surgeonis prompted to perform an RROM, which collects pose data from variouspre-determined leg motions and/or positions. From this data, the currenthip COR and patient's anatomical coordinate frame are extracted (forexample, by fitting pose data to geometrical models, using well-knownmathematical techniques). The anatomical coordinate frame willsubsequently be used to express pose measurements in terms of leg lengthand offset, rather than an arbitrary coordinate frame associated withthe sensor 202. The hip COR will subsequently be used to compensate forfemur orientation when calculating leg length and offset change.

After the completion of the RROM, the software automatically advances,and the workstation 218 (via the GUI) begins displaying real time andcontinuous leg length and offset change measurements to the surgeon(step 610), as previously shown in FIG. 5. The leg length and offsetchange measurements compensate for the current orientation of the femurby considering the baseline femur orientation, as well as the hip COR asdetermined in step 608; the system 200 compares the baseline pose withthe current (orientation-compensated) pose, and expresses the differencein the patient's anatomical coordinate frame, also determined in step608. The surgeon has the option to manually capture the data (as in step612), for example, via the user input associated with a “record”indicator 506. The surgeon has the option to end the program, as in step614, which may trigger a surgical data log on the workstation, once theyare pleased with the patient's leg length and offset. If there is achange in hip COR due to an acetabular side change (for example,changing liners, changing cup position, etc), the surgeon returns tostep 608 to repeat the RROM procedure (for example, via the user inputassociated with a “back” indicator 508), in order to recalculate the hipCOR. This is because the software compensates for femur orientation by“virtually rotating” it back to the baseline pose orientation, and usesthe acetabular hip COR as the pivot point for virtual rotation. Ratherthan returning to step 608 to repeat the RROM procedure, since thepatient's anatomical coordinate frame is not subject to change due to anacetabular COR positional change, an alternative method may include astep to calculate the new hip COR only (for example, by tracking thearticulation of the reduced hip joint). In a further alternativeembodiment, during step 610, the software may continuously estimate hipCOR to automatically detect if a change in hip COR position hasoccurred. This may be accomplished by tracking poses during a reduction,and relying on the constraint that during a given hip reduction, leglength and offset change measurements should not change.

Since the system 200 is a surgical device, sterility of the systemcomponents within the sterile field is important. Conventional methodsfor achieving sterility include: terminal sterilization (i.e. asingle-use disposable, sterilized with gamma radiation, ethylene oxide,etc), re-sterilization (via hospital processes, such as autoclaves), andbarrier/draping (i.e. a protective sterile barrier covering non-sterileequipment). With regard to system 200, the following components arepreferably either capable of re-sterilization, or are terminallysterile: beacon, femur platform, pelvic platform, pelvic clamp.Components such as bone screws and the target are well suited forterminal sterilization (to maintain their performance). The sensor maybe terminally sterilized, and provided as a single-use disposable item,or re-used with a sterile drape. Some commercially available steriledrape products are intended to be used with endoscopic cameras, andprovide an integrated optical “window”. (One example of a commerciallyavailable drape is a Closed System Camera Drape (PN 96-5204) from SklarInstruments, West Chester, Pa.) Such a drape may be preferred for usewith a non-sterile sensor 202 since the drape accommodates cablingthroughout, and facilitates optical sensing through the window, whilemaintaining a sterile barrier.

Where a sterile drape is used to maintain sensor sterility, the pelvicclamp may be configured to add another functional characteristic: toalign the drape window with the sensor optics. In FIG. 8A, an explodedview of a pelvic clamp assembly 800 is shown with a sterile drape 804.Pelvic clamp assembly 800 consists of sensor 202 and pelvic clamp 206,and optionally a shroud 806 and a sterile drape 804 The sterile drape804 maintains a sterile barrier between the non-sterile sensor 202 andthe surgical field. The shroud 806 (sterile) clamps, or fixes the sensor202 through the sterile drape 804, and an alignment feature 810 (e.g. aring clip) of the shroud 806 is used to align a drape window 812 withthe sensor's optical element 814. The shroud 806 (shown in a simplifiedmanner) has an outer surface 816 which matches a mating surface on theinside of the clamp 818. Each of the mating surfaces may define portionsof a sphere, such that the clamp/shroud interface provides an alignmentmechanism that is functionally a lockable ball joint. The clamp 206(sterile) has a mechanism (e.g. a screw/hinge combination) which appliesa force on the shroud 806 (and, in turn, the sensor 202), and clamps itrigidly and releasably in place. Hence the shroud and the clamp haverespective mating surfaces which, when the sensor is in the shroud andthe clamp is in a partially closed position, enable relative movement ofthe shroud and clamp to adjust the orientation of the sensor.

On the clamp 206 there is a quick connection mechanism 820, which isused to repeatably couple the sensor 202 with the pelvis 204 via thepelvic platform 208.

As components of system 200, the sensor 202 and pelvic clamp 206 may beused as follows. The non-sterile sensor 202 gets transferred into thesterile drape 804, according to the standard sterile draping techniquesfor which the sterile drape 804 is intended. Next, by sterile personnel,the sterile drape window 812 is manually aligned with the sensor opticalelement 814. Next, the shroud 806 is engaged with the sensor 202 throughthe sterile drape 804, such that the shroud engages the sensor 202 sothat the drape window 812 is held in place with respect to the sensoroptical element 814, using the shroud's alignment feature 810. Thesterile personnel may insert the assembly consisting of the shroud 806,sensor 202, and sterile drape 804 into the pelvic clamp 206, and performan alignment or aiming procedure, as described in steps 304 and 604. Theaiming may be performed manually, by grasping the back portion of thesensor 202 (exposed when inserted into pelvic clamp 206) andmanipulating its orientation. The assembly of FIG. 8 meets therequirements of: sterility, ability to aim sensor 202 (in 3degrees-of-freedom, due to the mating spherical surfaces) and lock thesensor 202 in place, maintaining optical performance, and providing aquick-connection mechanism to the pelvis.

In FIG. 8B, the pelvic clamp assembly 800 is shown in an assembledstate. When assembled, the shroud mates with the drape window in such away as to facilitate wiping (e.g. if debris ends up on the drape window,this could obscure the optics and interfere with operation of system200).

An example pelvic platform 900 (an example of platform 208) isillustrated in FIG. 9. There are three subcomponents: a screw 902, athumbnut 904, and a cannulated hub 906. The operation of this device isas follows. The screw gets driven into the pelvis, and the bone threads908 engage with the bone. The cannulated hub slides down the shaft ofthe screw until the spikes 910 contact bone (alternatively, thecannulated portion may be used as a dilator or guide for the screwinsertion). The thumbnut is advanced downward along the machine threads912, until it cinches the cannula spikes 910 (or alternatively referredto as teeth) into the bone. This device provides very rigid fixation,including torsional rigidity, using only a single stab incision. On topof the cannulated hub, there is a repeatable quick connection mechanism914 intended to mate with the pelvic clamp connection mechanism 820.

A femur platform 1000 (an example of femur platform 216) is shown inFIG. 10. The femur platform body 1002 is impacted into the femur(preferably the greater trochanter) and engages via the spikes 1004.Next, the femur screw 1006 is inserted through the femur platform bodyto cinch the assembly downward, and provide a very rigid structure. Thescrew length is such that it will not breach the femoral intra-medullarycanal, which would interfere with the surgeon's broaching process duringthe THA. On the femur platform body, there is a quick connect mechanism1008, which is used to connect the femur platform 1000 to a beacon 214,as described further below. The architecture of the femur platform isvery similar to the pelvic platform—there is a bone screw which cinchesdown spikes to form a rigid structure with a quick connection mechanism.

The quick connection mechanism (which interfaces the pelvic clamp 206and pelvic platform 208 and the beacon 214 and femur platform 216)facilitates a clear, un-crowded surgical site by allowing for therespective components to be removed when not in use (leaving behind theunobtrusive pelvic and femur platforms). FIG. 11A illustrates thedetails of an example quick connection mechanism with an isometric view,and FIG. 11B illustrates the details of the example quick connectionmechanism using a plan view. This example mechanism contains two matingcomponents: a first side 1100 and a second side 1102. Both first side1100 and second side 1102 mate via the combination of bull-nosed pins1104 and rails 1106, which provide a very repeatable contact surface.

The bull-nosed pin is a pin which terminates hemi-spherically, and therails provide two parallel contact surfaces which contact the pin on thehemispherical portion (i.e. the spacing between the rails is smallerthan the diameter of the hemisphere). The rails 1106 may be implementedusing dowel pins, or by machining slots, preferably chamfered, directlyinto the second side itself. Three pairs of bull-nosed pin 1104 andrails 1106 may be used for a repeatable connection; however, inpractice, this arrangement may not provide sufficient stability, inwhich case, four pairs may be used (as shown), while maintainingrepeatability through precise manufacturing tolerances. In addition toproviding a highly repeatable interface, the bull-nosed pin/railcombination provides a clearance distance between the first side 1100and second side 1102 of the quick connection; this is important forsurgical applications, as debris (e.g. blood, soft tissues, bonefragments) may soil the quick connection mechanism. By maintaining aclearance between both sides, the repeatable connection will maintainperformance in the presence of debris that would be typicallyencountered in surgery. Similarly, the bull-nosed pin and rail design istolerant of debris, since the pins and rails share a very small contactsurface.

In addition to aligning the two sides repeatably, the quick connectionrequires a force to keep the first side 1100 and second side 1102engaged. Many types of features may accomplish this; for example,springs, mating threads, cam-locks, etc. In FIG. 11B, complementarymagnets 1108 (on the first side 1100) and 1110 (on the second side 1102)are used to generate a coupling force. In the design shown, the magneticpolarity is such that the first side 1100 and second side 1102 willself-align when brought in close proximity to each other. Furthermore,the quick connection first side 1100 and second side 1102, includingrails 1106 and bull-nosed pins 1104, but excluding the first sidemagnets 1108 and second side magnets 1110, are preferably made fromnon-magnetic material. In this case, the first side 1100 and second side1102 will easily “snap” into place; this feature is very important tosurgeon-users, who value simplicity of use and confidence via positivetactile/audible feedback. Note that the two halves may be positioned inonly two orientations, 180 degrees from each other; this feature isimportant since it provides flexibility.

A beacon 214 with a mating quick connect mechanism is intended tointerface with the femur platform quick connection 1008 while rigidlyholding the target 210. With reference to FIG. 12, a beacon 1200 isshown (an example of beacon 214) with a quick connection mechanism 1202(in this case, a second side 1102) that interfaces with the femurplatform quick connection 1008 (in this case, a first side 1100). Thefront face 1204 is a holder for the target 210, which indicates properpositioning of the target 210 by its shape (see FIG. 13). The holder1204 has holding features 1206. The beacon 1200 provides a shaft 1208which may be easily gripped by a surgeon for attaching to and detachingfrom the femur platform 216 without touching, and hence risking soiling,the target 210. A top of the beacon 1210 includes a surface capable ofbeing impacted (e.g. hammered), which may be used to facilitate femurplatform 1000 initial installation (i.e. to engage the spikes 1004, butprior to screw 1006 fixation). In summary, the beacon 1200 holds thetarget 210, and may be attached to and detached from the patient's femur(via femur platform 216) repeatably by the surgeon, as required for thepurposes of using the system 200 for a THA.

The target 210 provides a precise and identifiable pattern for posetracking by the sensor during operation of system 200. Due to how thepattern is implemented and the precision required, the target 210 ispreferably a disposable system component. FIGS. 13A and 13B showrespective front 1300 and back 1302 sides of a planar target 210, inaccordance with an example. The back of the planar target 210 includesan attachment mechanism 1304 used to secure the target to the beaconattachment mechanism 1206 (for example, in this case, a combination ofslots and screws). The front of the target 210 has a pattern of markers1306. The pattern of markers (which could include lines, circles, etc)may employ redundancy, such that if the target is partially occluded bydebris (e.g. blood splatter), then the tracking system can stillfunction. The markers 1306 are identifiable to the sensor 202 and maycomprise a retro-reflective material (where the sensor 202 provides anillumination source). The markers are precisely positioned on the targetsubstrate 1308. Positioning may be accomplished using a laser cuttingprocedure, due to the accuracy of laser cutting. In this manufacturingprocedure, retro-reflective material is applied to cover the targetsubstrate 1308. A laser cutter is used to kiss-cut the desired pattern(e.g. which may be loaded into the laser cutter via a CAD file). Theexcess retro-reflective material is weeded off, leaving behind thedesired pattern. The target substrate 1308 may be of a black and diffusematerial; in other words, the material is good for absorbing andscattering light, particularly in the wavelengths of the tracking system(e.g. such as near infra-red) so that the marker 1306 signals are easilyidentifiable relative to the substrate 1308 (e.g. the substrate does notcause specular reflections from the illumination of the sensor).

An example sensor 1400 (for example for use as sensor 202) is shown inFIG. 14. It communicates to the workstation 218 via a cable 1402, oralternatively, wirelessly. The sensor has an optical element 1404, whichmay include infra-red filters. Also, the sensor may include anintegrated illuminator (not shown). The sensor contains a userinterface, comprising user inputs (i.e. buttons) 1406 and a userindicator (i.e. indicator LED's) 1408. The user interface (both userinputs 1406 and user indicator 1408) maintains its function through asterile drape 804. Having a user interface located within the sterilefield is a significant advantage, particularly over conventional passivecomputer navigation products; the surgeon may interact with the software220, rather than requiring verbal communication with non-sterilepersonnel. On the sensor enclosure 1410 there is a retaining feature1412, for example, a ridge, (also on the bottom face of enclosure 1410),which is used to locate, or position the shroud 806, without the risk ofcompromising the sterile drape 804 barrier. Note that the enclosure 1410also provides a locating feature (not shown) around the optical element1404, for the shroud 806 to properly align the sterile drape window 812with the optical element 1404. Internally, the sensor 1400 may storedata in non-volatile memory, including calibration parameters,manufacturing information and information to maintain data integrity.

The sensor 1400 contains one optical sensor, which includes a lens, animager, and possibly optical filters. Additionally, the sensor 1400 mayinclude an illuminator, in the case of tracking a non-active target 210.Based on the sensor model (i.e. the camera calibration), and based onthe art of monocular pose tracking, the sensor 1400 is able to providethe workstation 218 with sufficient sensor information to calculate thepose of a target 210, if the target 210 meets certain criteria (i.e. ifthe target 210 has a minimum of three identifiable features).

The workstation component can be any computing platform which canfacilitate the necessary computations to translate sensor output intopose, and then further process the poses, as well as provide a graphicaluser interface.

It may be advantageous to deviate from, or supplement, the softwareworkflow, as previously outlined in FIG. 6. A possible deviation wouldbe to perform a RROM procedure contemporaneously with the baselinemeasurement 606. This would facilitate: determining a pre-operative hipCOR and determining the patient's anatomical coordinate frame prior totrial reduction. The advantages of such an approach may include one ormore of:

-   -   obviating the need for the femur being neutrally positioned        during baseline;    -   facilitating acetabular cup positioning by tracking an impactor        in anatomical reference frame (by coupling another target to the        impactor);    -   quantifying change in hip COR position (from post-operative to        intra/post-operative).

Without performing an RROM contemporaneously with the baselinemeasurement, as suggested above, it is possible to position theacetabular cup under tracking guidance by repositioning the cup afterthe RROM procedure (FIG. 6, step 608). This may be done by starting witha trial cup, which is only loosely secured to the acetabulum, followedby a final cup, whose position is tracked via an additional target usingthe sensor 202, after the initial trial reduction. Similarly, theacetabular cup position may be verified after the RROM procedure, evenif it is not practicable to change its position (e.g., if a final cup isimpacted prior to RROM, its position can be verified). In any case,tracking the acetabular cup position may be done by attaching anadditional target (a second target, or using the existing target 210) tothe acetabular cup impactor in a known orientation.

It may be clinically beneficial to detect subluxation of the hip joint(an undesirable partial dislocation which occurs in certain orientationswithin the reduced range-of-motion). During step 610, the software andassociated method may be modified such that subluxation can be detectedand conveyed visually or audibly to the surgeon. This will allowsurgeons to identify subluxation (which is often too subtle to detect byeye), identify where in the range of motion subluxation occurs, and thentake corrective action. The premise is that system 200 compensates forfemur orientation when calculating the leg length and offset change, byconsidering the location of the hip COR. As a result, in a given rangeof motion (i.e. without changing the size of the implants), the legposition will remain constant, no matter how the femur is oriented;therefore, if system 200 detects a change in a leg position measurement,the reason would be joint subluxation (in other words, the ball is atleast partially coming out of the socket). The software 220 and method(step 610) could be modified to include a mode where, since the legposition should not change, apparent position changes are interpreted asjoint subluxation, and conveyed to the surgeon. In one embodiment, theworkstation 218 may alert in response to the detection, for exampleemitting an audible signal, or beep, when joint subluxation is detectedduring this mode. Using an audible signal would allow the surgeon tovisually focus on the hip joint, and gain a clinical understanding ofthe nature of the joint subluxation.

In another embodiment, the system and method may be further modified todetect joint subluxation. For example, the pre-dislocation baseline posemeasurement (in steps 304, 606) is not required to detect subluxation,meaning these steps may be omitted or modified accordingly. Similarly,calculating the map to the patient's anatomical coordinate frame (anobjective of the RROM procedure) is not required to detect subluxation(although it may be useful to quantify where within the replaced hiprange of motion subluxation occurs); however, it is preferable tocalculate the hip COR. This is because the subluxation measurementfundamentally relies on checking whether the radius (in 3D space) of thetarget 210 position to the hip COR has changed within a given range ofmotion of a given reduced hip joint.

During step 610, a “cone of stability” may be generated by tracking theorientation of the femur at extremes of its range-of-motion anddetecting poses where impingement or subluxation (as described above)may occur. This would allow the surgeon to assess whether the patient'srange-of-motion is adequate (for example, a young, active patient maydesire a large range of motion based on their day-to-day activities,whereas an elderly patient may not), and make clinical adjustments asnecessary. The “cone of stability” can be generated and conveyed to thesurgeon graphically, numerically, or in any other suitable manner. It ispreferable for the “cone of stability” to be conveyed with respect tothe patient's anatomical coordinate frame. The software 220 andassociated method (step 610) may be modified to include a“cone-of-stability” mode, where the tracking system pose data is used toassess the artificial joint, particularly at extremes of the jointsrange of motion; furthermore, the information may be displayed to asurgeon via display 222, in the patient's anatomical coordinate frame.

Accordingly, it is to be understood that this invention is not limitedto particular embodiments described, and as such may vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentinvention. Any recited method can be carried out in the order of eventsrecited or in any other order which is logically possible.

We claim:
 1. A system for alignment and repeatable attachment of asensor component comprising an optical sensor for use in a navigationalmedical procedure, the system comprising: a clamp comprising a bodyhaving a repeatable magnetic quick connect component, an inner surfaceand a clamping mechanism to facilitate clamping by the inner surface ofthe body; wherein the inner surface provides a component of an alignmentmechanism to cooperate with a mating surface for the sensor component,the alignment mechanism configured to orient the sensor component towarda site for the medical procedure prior to rigidly clamping the sensorcomponent in an oriented position via the inner surface using theclamping mechanism; and wherein the repeatable magnetic quick connectcomponent is configured to attach the clamp to a cooperating magneticquick connect component of a mounting platform.
 2. The system of claim 1wherein, when the sensor is at least partially within the clamp and theclamp is in a closed position, the clamping mechanism applies a forcethrough the inner surface toward the sensor component to hold the sensorrigidly and releasably in place; and wherein the inner surface providesa mating surface to a respective mating surface about the sensorcomponent such that, when the sensor component is at least partiallywithin the clamp and the clamp is in a partially closed position,relative movement of the sensor component and clamp adjusts theorientation of the sensor component toward a site for the medicalprocedure.
 3. The system of claim 2 further comprising a shroudconfigured to attach about the sensor component, the shroud comprisingthe respective mating surface for the sensor component.
 4. The system ofclaim 3 wherein the alignment mechanism comprises a lockable ball joint.5. The system of claim 1 wherein the alignment mechanism facilitatesorientation adjustment of the sensor in at least two degrees of freedom.6. The system of claim 1 wherein the alignment mechanism comprises alockable ball joint.
 7. The system of claim 1 wherein the mating surfacefor the sensor component is a partially spherical surface for matingwith a respective partially spherical surface provided by the innersurface of the clamp.
 8. The system of claim 1 wherein the repeatablemagnetic quick connect component comprises a first contact surface, thefirst contact surface configured to mate with a second contact surfaceof the cooperating magnetic quick connect component.
 9. The system ofclaim 8 wherein the first contact surface and the second contact surfacefurther comprise at least three pairs of mating slots and hemi-sphericalfeatures.
 10. The system of claim 8 wherein the repeatable magneticquick connect component further comprises at least three magnets. 11.The system of claim 8 further comprising the mounting platform.
 12. Thesystem of claim 11 wherein the mounting platform is configured to mountto a bone.
 13. The system of claim 12 wherein the bone is a pelvis. 14.The system of claim 1 further comprising a processing unit incommunication with the sensor component, the processing unit configuredto guide alignment of the sensor component, the processing unit usingpositional signals from the sensor component to calculate and display,using a user interface, directional instructions to move into alignmentthe sensor component with the site.
 15. The system of claim 1 furthercomprising a target to provide positional signals to the sensorcomponent.
 16. The system of claim 15 wherein the target has a secondrepeatable magnetic quick connect component.
 17. A clamp to align andrepeatably attach a sensor component comprising an optical sensor foruse in a navigational medical procedure, the clamp comprising: a bodyhaving an inner surface, a clamping mechanism to facilitate clamping bythe inner surface of the body; and a repeatable magnetic quick connectcomponent on the body; wherein the inner surface provides a component ofan alignment mechanism to cooperate with a mating surface for the sensorcomponent, the alignment mechanism configured to orient the sensorcomponent toward a site for the medical procedure prior to rigidlyclamping the sensor component in an oriented position via the innersurface using the clamping mechanism; and wherein the repeatablemagnetic quick connect component is configured to attach the clamp to acooperating magnetic quick connect component of a mounting platform. 18.The clamp of claim 17 wherein, when the sensor is at least partiallywithin the clamp and the clamp is in a closed position, the clampingmechanism applies a force through the inner surface toward the sensorcomponent to hold the sensor rigidly and releasably in place; andwherein the inner surface provides a mating surface to a respectivemating surface about the sensor component such that, when the sensorcomponent is at least partially within the clamp and the clamp is in apartially closed position, relative movement of the sensor component andclamp adjusts the orientation of the sensor component toward a site forthe medical procedure.
 19. The clamp of claim 18 wherein the innersurface is configured to mate with a shroud configured to attach aboutthe sensor component, the shroud comprising the respective matingsurface for the sensor component.
 20. The system of claim 1 wherein therepeatable magnetic quick connect component comprises a first contactsurface, the first contact surface configured to mate with a secondcontact surface of the cooperating magnetic quick connect component;wherein the first contact surface and the second contact surface furthercomprise at least three pairs of mating slots and hemi-sphericalfeatures and wherein the repeatable magnetic quick connect componentfurther comprises at least three magnets.